A rotary compressor conventionally available is described, for example, in Japanese Utility Model Laid-Open Publication No. 114082/1986. This conventional compressor, as illustrated in FIGS. 24 and 25, has a compression section A disposed within a sealed casing and driven by a motor. The compression section A comprises: a cylinder C having a cylinder chamber B; a roller E fitted to the eccentric shaft portion of a driving shaft D extending from the motor, so that the roller E orbits within the cylinder chamber B; and a blade H disposed at an intermediate portion between a suction port F and a discharge port G both provided in the cylinder C, the blade H being allowed to advance and retreat. The blade H is so arranged that part of the high-pressure gas discharged from the discharge port G acts on the rear side of the blade H as a back pressure to thereby bring the tip of the blade H normally in contact with part of the outer circumferential surface of the roller E, by which the cylinder chamber B is divided into a compression chamber X and a suction chamber Y. Further, the discharge port G is equipped with a plate-like discharge valve I that comes into contact with or disengages apart from the face of a valve seat formed around the exit of the discharge port G to thereby open or close the discharge port G.
With the above arrangement, while the roller E is being revolved within the cylinder chamber B with rotation of the driving shaft D, the gas in the compression chamber X within the cylinder chamber B defined by the blade H is compressed. When this compression process is completed to move to the discharge process, the compressed high-pressure gas is discharged from the discharge port G into the casing by an opening action of the discharge valve I. Then, when the discharge process is completed to move to the suction process, the discharge valve I is closed to thereby close the discharge port G, so that the low-pressure gas is sucked from the suction port F into the suction chamber Y within the cylinder chamber B defined by the blade H. In this way the compression and discharge processes are repeated.
However, with the above-described arrangement that the blade H is held to the cylinder C so as to be allowed to advance and retreat and is subject to a back pressure so that the tip of the blade H is brought into contact with the outer circumferential surface of the roller E, thus bringing the blade H and the roller E into relative movement therebetween, there Would arise a need of urging the tip of the blade H against the outer circumferential surface of the roller E by making a back pressure act on the blade H so that the tip of the blade H is in contact with the circumferential surface of the roller E. Moreover, the contact between the blade H and the outer circumferential surface of the roller E, which is a metal-to-metal contact without any intervening oil, would involve a great friction loss due to the sliding contact between the blade H and the outer circumferential surface of the roller E as well as a great power loss. What is more, because of the arrangement that a back pressure developed by the high-pressure gas discharged from the discharge port G is applied to the rear side of the blade H to bring the tip of the blade H into contact with the outer circumferential surface of the roller E, the high-pressure gas in the rear chamber of the blade H would leak into the suction chamber Y between a side face of the blade H and the blade's sliding recess, as indicated by an arrow a in FIG. 24, unfavorably resulting in a deteriorated volume efficiency. Also, since the compression chamber X varies from low to high pressure, an internal pressure in the compression chamber X lower than the back pressure would cause the high-pressure gas acting on the rear-side chamber to leak into the compression chamber X between a side face of the blade H and the blade's sliding recess, disadvantageously resulting in a lowered indication efficiency. Furthermore, there would be a possibility that the high-pressure gas compressed in the compression chamber X might leak into the suction chamber Y through the contact portion between the tip of the blade H and the roller E, as indicated by an arrow b in FIG. 24, which would add to the gas leak from the side faces of the blade H, resulting in a further lowered volume efficiency.